2 package Class::MOP::Class;
8 use Scalar::Util 'blessed', 'reftype';
9 use Sub::Name 'subname';
10 use B 'svref_2object';
12 our $VERSION = '0.14';
14 use Class::MOP::Instance;
18 sub meta { Class::MOP::Class->initialize(blessed($_[0]) || $_[0]) }
23 # Metaclasses are singletons, so we cache them here.
24 # there is no need to worry about destruction though
25 # because they should die only when the program dies.
26 # After all, do package definitions even get reaped?
29 # means of accessing all the metaclasses that have
30 # been initialized thus far (for mugwumps obj browser)
31 sub get_all_metaclasses { %METAS }
32 sub get_all_metaclass_instances { values %METAS }
33 sub get_all_metaclass_names { keys %METAS }
37 my $package_name = shift;
38 (defined $package_name && $package_name && !blessed($package_name))
39 || confess "You must pass a package name and it cannot be blessed";
40 $class->construct_class_instance(':package' => $package_name, @_);
45 my $package_name = shift;
46 (defined $package_name && $package_name && !blessed($package_name))
47 || confess "You must pass a package name and it cannot be blessed";
48 $METAS{$package_name} = undef;
49 $class->construct_class_instance(':package' => $package_name, @_);
52 # NOTE: (meta-circularity)
53 # this is a special form of &construct_instance
54 # (see below), which is used to construct class
55 # meta-object instances for any Class::MOP::*
56 # class. All other classes will use the more
57 # normal &construct_instance.
58 sub construct_class_instance {
61 my $package_name = $options{':package'};
62 (defined $package_name && $package_name)
63 || confess "You must pass a package name";
65 # return the metaclass if we have it cached,
66 # and it is still defined (it has not been
67 # reaped by DESTROY yet, which can happen
68 # annoyingly enough during global destruction)
69 return $METAS{$package_name}
70 if exists $METAS{$package_name} && defined $METAS{$package_name};
71 $class = blessed($class) || $class;
72 # now create the metaclass
74 if ($class =~ /^Class::MOP::/) {
76 '$:package' => $package_name,
78 '$:attribute_metaclass' => $options{':attribute_metaclass'} || 'Class::MOP::Attribute',
79 '$:method_metaclass' => $options{':method_metaclass'} || 'Class::MOP::Method',
80 '$:instance_metaclass' => $options{':instance_metaclass'} || 'Class::MOP::Instance',
85 # it is safe to use meta here because
86 # class will always be a subclass of
87 # Class::MOP::Class, which defines meta
88 $meta = bless $class->meta->construct_instance(%options) => $class
90 # and check the metaclass compatibility
91 $meta->check_metaclass_compatability();
92 $METAS{$package_name} = $meta;
95 sub check_metaclass_compatability {
98 # this is always okay ...
99 return if blessed($self) eq 'Class::MOP::Class' &&
100 $self->instance_metaclass eq 'Class::MOP::Instance';
102 my @class_list = $self->class_precedence_list;
103 shift @class_list; # shift off $self->name
105 foreach my $class_name (@class_list) {
106 my $meta = $METAS{$class_name} || next;
107 ($self->isa(blessed($meta)))
108 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
109 " is not compatible with the " .
110 $class_name . "->meta => (" . (blessed($meta)) . ")";
112 # we also need to check that instance metaclasses
113 # are compatabile in the same the class.
114 ($self->instance_metaclass->isa($meta->instance_metaclass))
115 || confess $self->name . "->meta => (" . ($self->instance_metaclass) . ")" .
116 " is not compatible with the " .
117 $class_name . "->meta => (" . ($meta->instance_metaclass) . ")";
123 my ($class, $package_name, $package_version, %options) = @_;
124 (defined $package_name && $package_name)
125 || confess "You must pass a package name";
126 my $code = "package $package_name;";
127 $code .= "\$$package_name\:\:VERSION = '$package_version';"
128 if defined $package_version;
130 confess "creation of $package_name failed : $@" if $@;
131 my $meta = $class->initialize($package_name);
133 $meta->add_method('meta' => sub {
134 Class::MOP::Class->initialize(blessed($_[0]) || $_[0]);
137 $meta->superclasses(@{$options{superclasses}})
138 if exists $options{superclasses};
140 # process attributes first, so that they can
141 # install accessors, but locally defined methods
142 # can then overwrite them. It is maybe a little odd, but
143 # I think this should be the order of things.
144 if (exists $options{attributes}) {
145 foreach my $attr (@{$options{attributes}}) {
146 $meta->add_attribute($attr);
149 if (exists $options{methods}) {
150 foreach my $method_name (keys %{$options{methods}}) {
151 $meta->add_method($method_name, $options{methods}->{$method_name});
159 # this should be sufficient, if you have a
160 # use case where it is not, write a test and
162 my $ANON_CLASS_SERIAL = 0;
164 sub create_anon_class {
165 my ($class, %options) = @_;
166 my $package_name = 'Class::MOP::Class::__ANON__::SERIAL::' . ++$ANON_CLASS_SERIAL;
167 return $class->create($package_name, '0.00', %options);
174 # all these attribute readers will be bootstrapped
175 # away in the Class::MOP bootstrap section
177 sub name { $_[0]->{'$:package'} }
178 sub get_attribute_map { $_[0]->{'%:attributes'} }
179 sub attribute_metaclass { $_[0]->{'$:attribute_metaclass'} }
180 sub method_metaclass { $_[0]->{'$:method_metaclass'} }
181 sub instance_metaclass { $_[0]->{'$:instance_metaclass'} }
183 # Instance Construction & Cloning
188 # we need to protect the integrity of the
189 # Class::MOP::Class singletons here, so we
190 # delegate this to &construct_class_instance
191 # which will deal with the singletons
192 return $class->construct_class_instance(@_)
193 if $class->name->isa('Class::MOP::Class');
194 return $class->construct_instance(@_);
197 sub construct_instance {
198 my ($class, %params) = @_;
199 my $meta_instance = $class->get_meta_instance();
200 my $instance = $meta_instance->create_instance();
201 foreach my $attr ($class->compute_all_applicable_attributes()) {
202 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
207 sub get_meta_instance {
209 return $class->instance_metaclass->new(
211 $class->compute_all_applicable_attributes()
217 my $instance = shift;
218 (blessed($instance) && $instance->isa($class->name))
219 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
221 # we need to protect the integrity of the
222 # Class::MOP::Class singletons here, they
223 # should not be cloned.
224 return $instance if $instance->isa('Class::MOP::Class');
225 $class->clone_instance($instance, @_);
229 my ($class, $instance, %params) = @_;
231 || confess "You can only clone instances, \$self is not a blessed instance";
232 my $meta_instance = $class->get_meta_instance();
233 my $clone = $meta_instance->clone_instance($instance);
234 foreach my $key (%params) {
235 next unless $meta_instance->is_valid_slot($key);
236 $meta_instance->set_slot_value($clone, $key, $params{$key});
243 # &name should be here too, but it is above
244 # because it gets bootstrapped away
248 ${$self->get_package_variable('$VERSION')};
258 @{$self->name . '::ISA'} = @supers;
260 # we need to check the metaclass
261 # compatability here so that we can
262 # be sure that the superclass is
263 # not potentially creating an issues
264 # we don't know about
265 $self->check_metaclass_compatability();
267 @{$self->name . '::ISA'};
270 sub class_precedence_list {
273 # We need to check for ciruclar inheirtance here.
274 # This will do nothing if all is well, and blow
275 # up otherwise. Yes, it's an ugly hack, better
276 # suggestions are welcome.
277 { ($self->name || return)->isa('This is a test for circular inheritance') }
278 # ... and now back to our regularly scheduled program
282 $self->initialize($_)->class_precedence_list()
283 } $self->superclasses()
290 my ($self, $method_name, $method) = @_;
291 (defined $method_name && $method_name)
292 || confess "You must define a method name";
293 # use reftype here to allow for blessed subs ...
294 ('CODE' eq (reftype($method) || ''))
295 || confess "Your code block must be a CODE reference";
296 my $full_method_name = ($self->name . '::' . $method_name);
298 $method = $self->method_metaclass->wrap($method) unless blessed($method);
301 no warnings 'redefine';
302 *{$full_method_name} = subname $full_method_name => $method;
306 my $fetch_and_prepare_method = sub {
307 my ($self, $method_name) = @_;
309 my $method = $self->get_method($method_name);
310 # if we dont have local ...
312 # make sure this method even exists ...
313 ($self->find_next_method_by_name($method_name))
314 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
315 # if so, then create a local which just
316 # calls the next applicable method ...
317 $self->add_method($method_name => sub {
318 $self->find_next_method_by_name($method_name)->(@_);
320 $method = $self->get_method($method_name);
323 # now make sure we wrap it properly
324 # (if it isnt already)
325 unless ($method->isa('Class::MOP::Method::Wrapped')) {
326 $method = Class::MOP::Method::Wrapped->wrap($method);
327 $self->add_method($method_name => $method);
332 sub add_before_method_modifier {
333 my ($self, $method_name, $method_modifier) = @_;
334 (defined $method_name && $method_name)
335 || confess "You must pass in a method name";
336 my $method = $fetch_and_prepare_method->($self, $method_name);
337 $method->add_before_modifier(subname ':before' => $method_modifier);
340 sub add_after_method_modifier {
341 my ($self, $method_name, $method_modifier) = @_;
342 (defined $method_name && $method_name)
343 || confess "You must pass in a method name";
344 my $method = $fetch_and_prepare_method->($self, $method_name);
345 $method->add_after_modifier(subname ':after' => $method_modifier);
348 sub add_around_method_modifier {
349 my ($self, $method_name, $method_modifier) = @_;
350 (defined $method_name && $method_name)
351 || confess "You must pass in a method name";
352 my $method = $fetch_and_prepare_method->($self, $method_name);
353 $method->add_around_modifier(subname ':around' => $method_modifier);
357 # the methods above used to be named like this:
358 # ${pkg}::${method}:(before|after|around)
359 # but this proved problematic when using one modifier
360 # to wrap multiple methods (something which is likely
361 # to happen pretty regularly IMO). So instead of naming
362 # it like this, I have chosen to just name them purely
363 # with their modifier names, like so:
364 # :(before|after|around)
365 # The fact is that in a stack trace, it will be fairly
366 # evident from the context what method they are attached
367 # to, and so don't need the fully qualified name.
371 my ($self, $method_name, $method) = @_;
372 (defined $method_name && $method_name)
373 || confess "You must define a method name";
374 # use reftype here to allow for blessed subs ...
375 ('CODE' eq (reftype($method) || ''))
376 || confess "Your code block must be a CODE reference";
377 my $full_method_name = ($self->name . '::' . $method_name);
379 $method = $self->method_metaclass->wrap($method) unless blessed($method);
382 no warnings 'redefine';
383 *{$full_method_name} = $method;
387 my ($self, $method_name) = @_;
388 (defined $method_name && $method_name)
389 || confess "You must define a method name";
391 my $sub_name = ($self->name . '::' . $method_name);
394 return 0 if !defined(&{$sub_name});
395 my $method = \&{$sub_name};
396 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
397 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
399 # at this point we are relatively sure
400 # it is our method, so we bless/wrap it
401 $self->method_metaclass->wrap($method) unless blessed($method);
406 my ($self, $method_name) = @_;
407 (defined $method_name && $method_name)
408 || confess "You must define a method name";
410 return unless $self->has_method($method_name);
413 return \&{$self->name . '::' . $method_name};
417 my ($self, $method_name) = @_;
418 (defined $method_name && $method_name)
419 || confess "You must define a method name";
421 my $removed_method = $self->get_method($method_name);
424 delete ${$self->name . '::'}{$method_name}
425 if defined $removed_method;
427 return $removed_method;
430 sub get_method_list {
433 grep { $self->has_method($_) } keys %{$self->name . '::'};
436 sub compute_all_applicable_methods {
439 # keep a record of what we have seen
440 # here, this will handle all the
441 # inheritence issues because we are
442 # using the &class_precedence_list
443 my (%seen_class, %seen_method);
444 foreach my $class ($self->class_precedence_list()) {
445 next if $seen_class{$class};
446 $seen_class{$class}++;
447 # fetch the meta-class ...
448 my $meta = $self->initialize($class);
449 foreach my $method_name ($meta->get_method_list()) {
450 next if exists $seen_method{$method_name};
451 $seen_method{$method_name}++;
453 name => $method_name,
455 code => $meta->get_method($method_name)
462 sub find_all_methods_by_name {
463 my ($self, $method_name) = @_;
464 (defined $method_name && $method_name)
465 || confess "You must define a method name to find";
467 # keep a record of what we have seen
468 # here, this will handle all the
469 # inheritence issues because we are
470 # using the &class_precedence_list
472 foreach my $class ($self->class_precedence_list()) {
473 next if $seen_class{$class};
474 $seen_class{$class}++;
475 # fetch the meta-class ...
476 my $meta = $self->initialize($class);
478 name => $method_name,
480 code => $meta->get_method($method_name)
481 } if $meta->has_method($method_name);
486 sub find_next_method_by_name {
487 my ($self, $method_name) = @_;
488 (defined $method_name && $method_name)
489 || confess "You must define a method name to find";
490 # keep a record of what we have seen
491 # here, this will handle all the
492 # inheritence issues because we are
493 # using the &class_precedence_list
495 my @cpl = $self->class_precedence_list();
496 shift @cpl; # discard ourselves
497 foreach my $class (@cpl) {
498 next if $seen_class{$class};
499 $seen_class{$class}++;
500 # fetch the meta-class ...
501 my $meta = $self->initialize($class);
502 return $meta->get_method($method_name)
503 if $meta->has_method($method_name);
512 # either we have an attribute object already
513 # or we need to create one from the args provided
514 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
515 # make sure it is derived from the correct type though
516 ($attribute->isa('Class::MOP::Attribute'))
517 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
518 $attribute->attach_to_class($self);
519 $attribute->install_accessors();
520 $self->get_attribute_map->{$attribute->name} = $attribute;
523 # in theory we have to tell everyone the slot structure may have changed
527 my ($self, $attribute_name) = @_;
528 (defined $attribute_name && $attribute_name)
529 || confess "You must define an attribute name";
530 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
534 my ($self, $attribute_name) = @_;
535 (defined $attribute_name && $attribute_name)
536 || confess "You must define an attribute name";
537 return $self->get_attribute_map->{$attribute_name}
538 if $self->has_attribute($attribute_name);
542 sub remove_attribute {
543 my ($self, $attribute_name) = @_;
544 (defined $attribute_name && $attribute_name)
545 || confess "You must define an attribute name";
546 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
547 return unless defined $removed_attribute;
548 delete $self->get_attribute_map->{$attribute_name};
549 $removed_attribute->remove_accessors();
550 $removed_attribute->detach_from_class();
551 return $removed_attribute;
554 sub get_attribute_list {
556 keys %{$self->get_attribute_map};
559 sub compute_all_applicable_attributes {
562 # keep a record of what we have seen
563 # here, this will handle all the
564 # inheritence issues because we are
565 # using the &class_precedence_list
566 my (%seen_class, %seen_attr);
567 foreach my $class ($self->class_precedence_list()) {
568 next if $seen_class{$class};
569 $seen_class{$class}++;
570 # fetch the meta-class ...
571 my $meta = $self->initialize($class);
572 foreach my $attr_name ($meta->get_attribute_list()) {
573 next if exists $seen_attr{$attr_name};
574 $seen_attr{$attr_name}++;
575 push @attrs => $meta->get_attribute($attr_name);
581 sub find_attribute_by_name {
582 my ($self, $attr_name) = @_;
583 # keep a record of what we have seen
584 # here, this will handle all the
585 # inheritence issues because we are
586 # using the &class_precedence_list
588 foreach my $class ($self->class_precedence_list()) {
589 next if $seen_class{$class};
590 $seen_class{$class}++;
591 # fetch the meta-class ...
592 my $meta = $self->initialize($class);
593 return $meta->get_attribute($attr_name)
594 if $meta->has_attribute($attr_name);
601 sub add_package_variable {
602 my ($self, $variable, $initial_value) = @_;
603 (defined $variable && $variable =~ /^[\$\@\%]/)
604 || confess "variable name does not have a sigil";
606 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
607 if (defined $initial_value) {
609 *{$self->name . '::' . $name} = $initial_value;
615 # We HAVE to localize $@ or all
616 # hell breaks loose. It is not
617 # good, believe me, not good.
619 eval $sigil . $self->name . '::' . $name;
622 confess "Could not create package variable ($variable) because : $e" if $e;
626 sub has_package_variable {
627 my ($self, $variable) = @_;
628 (defined $variable && $variable =~ /^[\$\@\%]/)
629 || confess "variable name does not have a sigil";
630 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
632 defined ${$self->name . '::'}{$name} ? 1 : 0;
635 sub get_package_variable {
636 my ($self, $variable) = @_;
637 (defined $variable && $variable =~ /^[\$\@\%]/)
638 || confess "variable name does not have a sigil";
639 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
643 # We HAVE to localize $@ or all
644 # hell breaks loose. It is not
645 # good, believe me, not good.
647 $ref = eval '\\' . $sigil . $self->name . '::' . $name;
650 confess "Could not get the package variable ($variable) because : $e" if $e;
651 # if we didn't die, then we can return it
655 sub remove_package_variable {
656 my ($self, $variable) = @_;
657 (defined $variable && $variable =~ /^[\$\@\%]/)
658 || confess "variable name does not have a sigil";
659 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
661 delete ${$self->name . '::'}{$name};
672 Class::MOP::Class - Class Meta Object
676 # assuming that class Foo
677 # has been defined, you can
679 # use this for introspection ...
681 # add a method to Foo ...
682 Foo->meta->add_method('bar' => sub { ... })
684 # get a list of all the classes searched
685 # the method dispatcher in the correct order
686 Foo->meta->class_precedence_list()
688 # remove a method from Foo
689 Foo->meta->remove_method('bar');
691 # or use this to actually create classes ...
693 Class::MOP::Class->create('Bar' => '0.01' => (
694 superclasses => [ 'Foo' ],
696 Class::MOP:::Attribute->new('$bar'),
697 Class::MOP:::Attribute->new('$baz'),
700 calculate_bar => sub { ... },
701 construct_baz => sub { ... }
707 This is the largest and currently most complex part of the Perl 5
708 meta-object protocol. It controls the introspection and
709 manipulation of Perl 5 classes (and it can create them too). The
710 best way to understand what this module can do, is to read the
711 documentation for each of it's methods.
715 =head2 Self Introspection
721 This will return a B<Class::MOP::Class> instance which is related
722 to this class. Thereby allowing B<Class::MOP::Class> to actually
725 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
726 bootstrap this module by installing a number of attribute meta-objects
727 into it's metaclass. This will allow this class to reap all the benifits
728 of the MOP when subclassing it.
730 =item B<get_all_metaclasses>
732 This will return an hash of all the metaclass instances that have
733 been cached by B<Class::MOP::Class> keyed by the package name.
735 =item B<get_all_metaclass_instances>
737 This will return an array of all the metaclass instances that have
738 been cached by B<Class::MOP::Class>.
740 =item B<get_all_metaclass_names>
742 This will return an array of all the metaclass names that have
743 been cached by B<Class::MOP::Class>.
747 =head2 Class construction
749 These methods will handle creating B<Class::MOP::Class> objects,
750 which can be used to both create new classes, and analyze
751 pre-existing classes.
753 This module will internally store references to all the instances
754 you create with these methods, so that they do not need to be
755 created any more than nessecary. Basically, they are singletons.
759 =item B<create ($package_name, ?$package_version,
760 superclasses =E<gt> ?@superclasses,
761 methods =E<gt> ?%methods,
762 attributes =E<gt> ?%attributes)>
764 This returns a B<Class::MOP::Class> object, bringing the specified
765 C<$package_name> into existence and adding any of the
766 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
769 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
770 methods =E<gt> ?%methods,
771 attributes =E<gt> ?%attributes)>
773 This will create an anonymous class, it works much like C<create> but
774 it does not need a C<$package_name>. Instead it will create a suitably
775 unique package name for you to stash things into.
777 =item B<initialize ($package_name)>
779 This initializes and returns returns a B<Class::MOP::Class> object
780 for a given a C<$package_name>.
782 =item B<construct_class_instance (%options)>
784 This will construct an instance of B<Class::MOP::Class>, it is
785 here so that we can actually "tie the knot" for B<Class::MOP::Class>
786 to use C<construct_instance> once all the bootstrapping is done. This
787 method is used internally by C<initialize> and should never be called
788 from outside of that method really.
790 =item B<check_metaclass_compatability>
792 This method is called as the very last thing in the
793 C<construct_class_instance> method. This will check that the
794 metaclass you are creating is compatible with the metaclasses of all
795 your ancestors. For more inforamtion about metaclass compatibility
796 see the C<About Metaclass compatibility> section in L<Class::MOP>.
800 =head2 Object instance construction and cloning
802 These methods are B<entirely optional>, it is up to you whether you want
807 =item B<instance_metaclass>
809 =item B<get_meta_instance>
811 =item B<new_object (%params)>
813 This is a convience method for creating a new object of the class, and
814 blessing it into the appropriate package as well. Ideally your class
815 would call a C<new> this method like so:
818 my ($class, %param) = @_;
819 $class->meta->new_object(%params);
822 Of course the ideal place for this would actually be in C<UNIVERSAL::>
823 but that is considered bad style, so we do not do that.
825 =item B<construct_instance (%params)>
827 This method is used to construct an instace structure suitable for
828 C<bless>-ing into your package of choice. It works in conjunction
829 with the Attribute protocol to collect all applicable attributes.
831 This will construct and instance using a HASH ref as storage
832 (currently only HASH references are supported). This will collect all
833 the applicable attributes and layout out the fields in the HASH ref,
834 it will then initialize them using either use the corresponding key
835 in C<%params> or any default value or initializer found in the
836 attribute meta-object.
838 =item B<clone_object ($instance, %params)>
840 This is a convience method for cloning an object instance, then
841 blessing it into the appropriate package. This method will call
842 C<clone_instance>, which performs a shallow copy of the object,
843 see that methods documentation for more details. Ideally your
844 class would call a C<clone> this method like so:
847 my ($self, %param) = @_;
848 $self->meta->clone_object($self, %params);
851 Of course the ideal place for this would actually be in C<UNIVERSAL::>
852 but that is considered bad style, so we do not do that.
854 =item B<clone_instance($instance, %params)>
856 This method is a compliment of C<construct_instance> (which means if
857 you override C<construct_instance>, you need to override this one too),
858 and clones the instance shallowly.
860 The cloned structure returned is (like with C<construct_instance>) an
861 unC<bless>ed HASH reference, it is your responsibility to then bless
862 this cloned structure into the right class (which C<clone_object> will
865 As of 0.11, this method will clone the C<$instance> structure shallowly,
866 as opposed to the deep cloning implemented in prior versions. After much
867 thought, research and discussion, I have decided that anything but basic
868 shallow cloning is outside the scope of the meta-object protocol. I
869 think Yuval "nothingmuch" Kogman put it best when he said that cloning
870 is too I<context-specific> to be part of the MOP.
880 This is a read-only attribute which returns the package name for the
881 given B<Class::MOP::Class> instance.
885 This is a read-only attribute which returns the C<$VERSION> of the
886 package for the given B<Class::MOP::Class> instance.
890 =head2 Inheritance Relationships
894 =item B<superclasses (?@superclasses)>
896 This is a read-write attribute which represents the superclass
897 relationships of the class the B<Class::MOP::Class> instance is
898 associated with. Basically, it can get and set the C<@ISA> for you.
901 Perl will occasionally perform some C<@ISA> and method caching, if
902 you decide to change your superclass relationship at runtime (which
903 is quite insane and very much not recommened), then you should be
904 aware of this and the fact that this module does not make any
905 attempt to address this issue.
907 =item B<class_precedence_list>
909 This computes the a list of all the class's ancestors in the same order
910 in which method dispatch will be done. This is similair to
911 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
919 =item B<method_metaclass>
921 =item B<add_method ($method_name, $method)>
923 This will take a C<$method_name> and CODE reference to that
924 C<$method> and install it into the class's package.
927 This does absolutely nothing special to C<$method>
928 other than use B<Sub::Name> to make sure it is tagged with the
929 correct name, and therefore show up correctly in stack traces and
932 =item B<alias_method ($method_name, $method)>
934 This will take a C<$method_name> and CODE reference to that
935 C<$method> and alias the method into the class's package.
938 Unlike C<add_method>, this will B<not> try to name the
939 C<$method> using B<Sub::Name>, it only aliases the method in
942 =item B<has_method ($method_name)>
944 This just provides a simple way to check if the class implements
945 a specific C<$method_name>. It will I<not> however, attempt to check
946 if the class inherits the method (use C<UNIVERSAL::can> for that).
948 This will correctly handle functions defined outside of the package
949 that use a fully qualified name (C<sub Package::name { ... }>).
951 This will correctly handle functions renamed with B<Sub::Name> and
952 installed using the symbol tables. However, if you are naming the
953 subroutine outside of the package scope, you must use the fully
954 qualified name, including the package name, for C<has_method> to
955 correctly identify it.
957 This will attempt to correctly ignore functions imported from other
958 packages using B<Exporter>. It breaks down if the function imported
959 is an C<__ANON__> sub (such as with C<use constant>), which very well
960 may be a valid method being applied to the class.
962 In short, this method cannot always be trusted to determine if the
963 C<$method_name> is actually a method. However, it will DWIM about
964 90% of the time, so it's a small trade off I think.
966 =item B<get_method ($method_name)>
968 This will return a CODE reference of the specified C<$method_name>,
969 or return undef if that method does not exist.
971 =item B<remove_method ($method_name)>
973 This will attempt to remove a given C<$method_name> from the class.
974 It will return the CODE reference that it has removed, and will
975 attempt to use B<Sub::Name> to clear the methods associated name.
977 =item B<get_method_list>
979 This will return a list of method names for all I<locally> defined
980 methods. It does B<not> provide a list of all applicable methods,
981 including any inherited ones. If you want a list of all applicable
982 methods, use the C<compute_all_applicable_methods> method.
984 =item B<compute_all_applicable_methods>
986 This will return a list of all the methods names this class will
987 respond to, taking into account inheritance. The list will be a list of
988 HASH references, each one containing the following information; method
989 name, the name of the class in which the method lives and a CODE
990 reference for the actual method.
992 =item B<find_all_methods_by_name ($method_name)>
994 This will traverse the inheritence hierarchy and locate all methods
995 with a given C<$method_name>. Similar to
996 C<compute_all_applicable_methods> it returns a list of HASH references
997 with the following information; method name (which will always be the
998 same as C<$method_name>), the name of the class in which the method
999 lives and a CODE reference for the actual method.
1001 The list of methods produced is a distinct list, meaning there are no
1002 duplicates in it. This is especially useful for things like object
1003 initialization and destruction where you only want the method called
1004 once, and in the correct order.
1006 =item B<find_next_method_by_name ($method_name)>
1008 This will return the first method to match a given C<$method_name> in
1009 the superclasses, this is basically equivalent to calling
1010 C<SUPER::$method_name>, but it can be dispatched at runtime.
1014 =head2 Method Modifiers
1016 Method modifiers are a concept borrowed from CLOS, in which a method
1017 can be wrapped with I<before>, I<after> and I<around> method modifiers
1018 that will be called everytime the method is called.
1020 =head3 How method modifiers work?
1022 Method modifiers work by wrapping the original method and then replacing
1023 it in the classes symbol table. The wrappers will handle calling all the
1024 modifiers in the appropariate orders and preserving the calling context
1025 for the original method.
1027 Each method modifier serves a particular purpose, which may not be
1028 obvious to users of other method wrapping modules. To start with, the
1029 return values of I<before> and I<after> modifiers are ignored. This is
1030 because thier purpose is B<not> to filter the input and output of the
1031 primary method (this is done with an I<around> modifier). This may seem
1032 like an odd restriction to some, but doing this allows for simple code
1033 to be added at the begining or end of a method call without jeapordizing
1034 the normal functioning of the primary method or placing any extra
1035 responsibility on the code of the modifier. Of course if you have more
1036 complex needs, then use the I<around> modifier, which uses a variation
1037 of continutation passing style to allow for a high degree of flexibility.
1039 Before and around modifiers are called in last-defined-first-called order,
1040 while after modifiers are called in first-defined-first-called order. So
1041 the call tree might looks something like this:
1051 To see examples of using method modifiers, see the following examples
1052 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1053 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1054 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1056 =head3 What is the performance impact?
1058 Of course there is a performance cost associated with method modifiers,
1059 but we have made every effort to make that cost be directly proportional
1060 to the amount of modifier features you utilize.
1062 The wrapping method does it's best to B<only> do as much work as it
1063 absolutely needs to. In order to do this we have moved some of the
1064 performance costs to set-up time, where they are easier to amortize.
1066 All this said, my benchmarks have indicated the following:
1068 simple wrapper with no modifiers 100% slower
1069 simple wrapper with simple before modifier 400% slower
1070 simple wrapper with simple after modifier 450% slower
1071 simple wrapper with simple around modifier 500-550% slower
1072 simple wrapper with all 3 modifiers 1100% slower
1074 These numbers may seem daunting, but you must remember, every feature
1075 comes with some cost. To put things in perspective, just doing a simple
1076 C<AUTOLOAD> which does nothing but extract the name of the method called
1077 and return it costs about 400% over a normal method call.
1081 =item B<add_before_method_modifier ($method_name, $code)>
1083 This will wrap the method at C<$method_name> and the supplied C<$code>
1084 will be passed the C<@_> arguments, and called before the original
1085 method is called. As specified above, the return value of the I<before>
1086 method modifiers is ignored, and it's ability to modify C<@_> is
1087 fairly limited. If you need to do either of these things, use an
1088 C<around> method modifier.
1090 =item B<add_after_method_modifier ($method_name, $code)>
1092 This will wrap the method at C<$method_name> so that the original
1093 method will be called, it's return values stashed, and then the
1094 supplied C<$code> will be passed the C<@_> arguments, and called.
1095 As specified above, the return value of the I<after> method
1096 modifiers is ignored, and it cannot modify the return values of
1097 the original method. If you need to do either of these things, use an
1098 C<around> method modifier.
1100 =item B<add_around_method_modifier ($method_name, $code)>
1102 This will wrap the method at C<$method_name> so that C<$code>
1103 will be called and passed the original method as an extra argument
1104 at the begining of the C<@_> argument list. This is a variation of
1105 continuation passing style, where the function prepended to C<@_>
1106 can be considered a continuation. It is up to C<$code> if it calls
1107 the original method or not, there is no restriction on what the
1108 C<$code> can or cannot do.
1114 It should be noted that since there is no one consistent way to define
1115 the attributes of a class in Perl 5. These methods can only work with
1116 the information given, and can not easily discover information on
1117 their own. See L<Class::MOP::Attribute> for more details.
1121 =item B<attribute_metaclass>
1123 =item B<get_attribute_map>
1125 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1127 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1128 instance associated with the given class, and associates it with
1129 the C<$attribute_name>. Unlike methods, attributes within the MOP
1130 are stored as meta-information only. They will be used later to
1131 construct instances from (see C<construct_instance> above).
1132 More details about the attribute meta-objects can be found in the
1133 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1136 It should be noted that any accessor, reader/writer or predicate
1137 methods which the C<$attribute_meta_object> has will be installed
1138 into the class at this time.
1140 =item B<has_attribute ($attribute_name)>
1142 Checks to see if this class has an attribute by the name of
1143 C<$attribute_name> and returns a boolean.
1145 =item B<get_attribute ($attribute_name)>
1147 Returns the attribute meta-object associated with C<$attribute_name>,
1148 if none is found, it will return undef.
1150 =item B<remove_attribute ($attribute_name)>
1152 This will remove the attribute meta-object stored at
1153 C<$attribute_name>, then return the removed attribute meta-object.
1156 Removing an attribute will only affect future instances of
1157 the class, it will not make any attempt to remove the attribute from
1158 any existing instances of the class.
1160 It should be noted that any accessor, reader/writer or predicate
1161 methods which the attribute meta-object stored at C<$attribute_name>
1162 has will be removed from the class at this time. This B<will> make
1163 these attributes somewhat inaccessable in previously created
1164 instances. But if you are crazy enough to do this at runtime, then
1165 you are crazy enough to deal with something like this :).
1167 =item B<get_attribute_list>
1169 This returns a list of attribute names which are defined in the local
1170 class. If you want a list of all applicable attributes for a class,
1171 use the C<compute_all_applicable_attributes> method.
1173 =item B<compute_all_applicable_attributes>
1175 This will traverse the inheritance heirachy and return a list of all
1176 the applicable attributes for this class. It does not construct a
1177 HASH reference like C<compute_all_applicable_methods> because all
1178 that same information is discoverable through the attribute
1181 =item B<find_attribute_by_name ($attr_name)>
1183 This method will traverse the inheritance heirachy and find the
1184 first attribute whose name matches C<$attr_name>, then return it.
1185 It will return undef if nothing is found.
1189 =head2 Package Variables
1191 Since Perl's classes are built atop the Perl package system, it is
1192 fairly common to use package scoped variables for things like static
1193 class variables. The following methods are convience methods for
1194 the creation and inspection of package scoped variables.
1198 =item B<add_package_variable ($variable_name, ?$initial_value)>
1200 Given a C<$variable_name>, which must contain a leading sigil, this
1201 method will create that variable within the package which houses the
1202 class. It also takes an optional C<$initial_value>, which must be a
1203 reference of the same type as the sigil of the C<$variable_name>
1206 =item B<get_package_variable ($variable_name)>
1208 This will return a reference to the package variable in
1211 =item B<has_package_variable ($variable_name)>
1213 Returns true (C<1>) if there is a package variable defined for
1214 C<$variable_name>, and false (C<0>) otherwise.
1216 =item B<remove_package_variable ($variable_name)>
1218 This will attempt to remove the package variable at C<$variable_name>.
1224 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1226 =head1 COPYRIGHT AND LICENSE
1228 Copyright 2006 by Infinity Interactive, Inc.
1230 L<http://www.iinteractive.com>
1232 This library is free software; you can redistribute it and/or modify
1233 it under the same terms as Perl itself.